This program has three objectives: (1) the derivation, development, characterization, and applications of new strains and species of germfree animals which are needed for studies on diseases of biomedical importance. Of immediate concern are Buffalo strain rats, hamsters, and marmosets. (2) The propagation, maintenance, and characterization of eight strains of germfree mice and three strains of germfree rats with the aim of development and applications as model systems for diseases of biomedical importance. These will include gerontology, allogeneic chimerism, cancer therapy, and environmental pollutants. (3) Provision of facilities, germfree animals, and consultation services to investigators whose programs include germfree technology. The majority of the latter will be recipients of government support. By providing broad support for animal experimentation and development, the costs of all other programs involving animals have been markedly reduced. This type of support obviates the need for duplicate support structures for each research program and provides a unique flexibility for "open-ended" type requirements.